Tunable device, method of manufacture, and method of tuning a laser

ABSTRACT

This description relates to an apparatus, a method of manufacturing, and a method of tuning optical and/or electrical parameters of semiconductor devices and materials, thin film materials, or other devices. In one example, a laser is tuned to produce an adjustable output wavelength by coupling the laser to a tuning material or base such as, for example, a piezoelectric base using a suitable attachment method. The laser includes of a tunable material that is sensitive to stress and/or strain. Stress and/or strain applied to the laser from the tuning material results in an electronically variable output wavelength. As an example, applying a voltage to a piezoelectric base that serves as a tuning material can cause the base to expand or contract, and the expansions and contractions from the base are coupled to the tunable material of the laser, thus varying the wavelength of the output light from the laser. Additionally, other devices that are sensitive to stress and/or strain can be adjoined in a similar manner and can result in an electronically variable output of the devices. Examples of other embodiments are also disclosed herein.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application of U.S. patent application Ser. No.11/938,637 filed Nov. 12, 2007, which claims the benefit of U.S.Provisional Patent Application No. 60/865,610 filed Nov. 13, 2006. Thecontents of U.S. patent application Ser. No. 11/938,637 and U.S.Provisional Patent Application No. 60/865,610 are hereby incorporated byreference.

TECHNICAL FIELD

This description relates generally to adjusting output parameters of adevice and more particularly to apparatuses and methods of tuningoptical and electrical parameters of semiconductor devices andmaterials, or thin film materials or other devices.

BACKGROUND

Lasers are devices that can produce intense narrowly divergent,substantially single wavelength (monochromatic), coherent light. Laserlight of different wavelengths can be advantageously applied in manyfields, including biological, medical, military, space, industrial,commercial, computer, and telecommunications.

Semiconductor lasers may utilize an active region, which may be formedwith a homojunction (using similar materials), single or doubleheterojunction using dissimilar materials), or with a quantum well(“QW”) or quantum cascade region. The quantum well structure may beformed when a low energy bandgap semiconductor material is typicallypositioned between two large bandgap semiconductor materials.

In order for lasing to occur, a laser device typically has a resonantcavity and a gain medium to create population inversion. In highlyefficient semiconductor lasers, population inversion generally occurswith the injection of electrical carriers into the active region, andthe resonant cavity is typically formed by a pair of mirrors thatsurround the gain medium. The method of injection of carriers can bedivided into electrical injection of carriers and optical pumping forinjection of carriers. Electrical injection is generally performed by anelectrical current or voltage biasing of the laser. Optical pumpingtypically uses incident radiation that will allow the formation ofelectrons and holes in the laser. Additionally these methods can beoperated in a continuous wave (CW) pulsed, synchronous or asynchronousmodes.

Two common types of semiconductor lasers are in-plane, also known asedge emitting or Fabry Perot lasers, and surface emitting also known asvertical cavity surface emitting lasers (“VCSELs”). Edge emitting lasersemit light from the edge of the semiconductor wafer. In addition theresonant cavity is typically formed with cleaved mirrors at each end ofthe active region. The second type of semiconductor laser, VCSELs, emitslight normal to the surface of the semiconductor wafer. The resonantoptical cavity of a VCSEL may be formed with two sets of distributedBragg reflector mirrors located at the top and bottom of the laserstructure. The fundamental wavelength that characterizes quantum welland quantum cascade lasers is determined primarily by the thickness,composition and material of the quantum well.

However these lasers are typically limited to primarily one wavelength,thus the ability to create one laser that can produce many differentwavelengths controllably and accurately could be very useful for manyapplications, such as in the field of telecommunications. A tunablelaser could also be very useful in high data rate telecommunicationsapplications like dense wavelength division multiplexing, which may beused in fiber optic communications.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a tunable device assembly.

FIG. 2 shows tunable laser assembly.

FIG. 3 shows a first example of a tunable laser assembly formechanically stress-straining a laser to change its output wavelength oflight.

FIG. 4 shows a second example of a tunable laser assembly forelectronically stress-straining the laser in the lateral direction.

FIG. 5 shows a third example of a tunable laser assembly forelectronically stress-straining the laser in a bending, twisting ortorquing manner.

FIG. 6A shows a fourth example of a tunable laser assembly formechanically and electronically stress-straining the laser using atuning material and clamp.

FIG. 6B shows three additional examples of a tunable laser assemblyemploying two piezoelectrics for enhanced stress-strain effects.

FIG. 6C shows four additional examples of a tunable laser assemblyemploying a piezoelectric in combination with a MEMS, magneto-elastic,micro-fluidics or pressure producing device.

FIG. 7 shows a perspective view of an example of a semiconductor edgeemitting laser for use in the tunable laser assembly.

FIG. 8 shows a side view of an example of the vertical cavity surfaceemitting laser for use in the tunable laser assembly.

FIG. 9 shows two examples of the tuning apparatus of the tunable deviceassembly for applying stress-strain mechanically.

FIG. 10A shows tuning material properties and some of thecharacteristics of tuning material deformation upon application of avoltage.

FIG. 10B is a side cross-sectional views of two typical configurationsof tuning material made from a piezoelectric material.

FIG. 11 shows a flow chart of a method of combining the tuning materialwith the laser or other tunable material within a mechanical jig thatallows for deformation of a tunable laser or other tunable device.

FIG. 12 illustrates an exemplary epitaxial layer lift-off/bondingtechnique.

FIG. 13 is a flow chart of the epitaxial lift-off/bonding method.

FIG. 14 shows merging the semiconductor laser and the tuning material byan alternative process of wafer bonding.

FIG. 15 is a flow chart showing the method of direct merging of thelaser and the tuning material by wafer bonding.

FIG. 16 is a flow chart describing a method of direct deposition 1600 ofsemiconductor or thin film material on the tuning material(piezoelectric), to form a tunable device assembly, without directbonding or epitaxial lift-off.

FIG. 17 shows an example of a tunable device assembly to make a variablegain transistor.

FIG. 18 shows a schematic block diagram of a tunable laser assembly plusstrain gage feedback control.

FIG. 19 shows a block diagram of a tunable laser plus thermoelectrictemperature feedback control.

FIG. 20 shows a block diagram of the possible uses of the tunable laserassembly for applications in telecommunications.

For simplicity and clarity of illustration, the drawing figuresillustrate the general manner of construction, and descriptions anddetails of well-known features and techniques may be omitted to avoidunnecessarily obscuring the examples of the invention. Additionally,elements in the drawing figures are not necessarily drawn to scale. Forexample, the dimensions of some of the elements in the figures may beexaggerated relative to other elements to help improve understanding ofthe examples presented. Like reference numerals are used to designatelike parts in the accompanying drawings.

DETAILED DESCRIPTION

The description below describes the tuning of the output of a device bythe application of a stress and/or strain on the device. The examplesbelow include descriptions of examples of a tunable laser, methods forproducing a tunable laser, methods for tuning a laser, and systems thatmay use a tunable laser. In particular this description presentsexamples of a generalized apparatus and method of tuning optical andelectrical parameters of semiconductor devices and materials or thinfilm materials or devices (where thin film may refer to polymer, liquidcrystal, organic materials or the like). Some examples specificallydescribe tuning the wavelength of light emitted from semiconductorlasers in a controllable and predictable manner. However it iscontemplated that the techniques described below may also be applied tovarying other parameters that are sensitive to stress/strain, forexample possibly varying the gain of a transistor where the gain issensitive to pressure applied to the semiconductor material.

Some of the examples described disclose a unique apparatus and methodfor making a monolithic or compact tunable wavelength laser. Theexamples disclosed may provide two functions, 1) production of laserlight and 2) a way of tuning the laser light produced within thesemiconductor laser itself. These examples typically show that it may bepossible to eliminate an external cavity that might be used to tune thewavelength in conventional systems, thus providing tunability of asemiconductor laser in a monolithic or compact manner. Also theseexamples typically provide a relatively temperature insensitive methodof tuning the wavelength of the laser, which usually allows for veryfast wavelength changes.

In conventional systems a variety of wavelengths can be produced in acontrollable manner from a single laser source when two components areused 1) a laser to produce laser light characterized by a fundamentalwavelength and 2) a separate external cavity to change the wavelength ofthe laser light. The external cavity in current technologies hasgenerally resulted in increased costs, process complexity, and size.

In the present examples the wavelength of the light emitted from theactive region of the semiconductor laser can be varied away from thefundamental wavelength of the laser without an external resonant cavity.Thus the tuning of the wavelength may achieved by a tuning device intypically integral or in close contact with the semiconductor laserdevice. Because external tuning is not needed, the tunable laser may beclose to the size and dimension of the semiconductor laser. Also, such acompact device tends to be cost effective and economical to produce. Thetunable laser may employ an exemplary laser which can be coupled to atuning material, such as an exemplary piezoelectric base, a mechanicalpressure or stress system, a Micro-Electro-Mechanical Systems (“MEMS”),a magneto-elastic, micro-fluidics or equivalent, by use of a suitablebonding, coupling or adjoining method. For example by applying a voltageto the piezoelectric base, expansion and contractions can be created,which may be coupled to the semiconductor laser, thus altering theemitted wavelength of light. Many of the attendant features will be morereadily appreciated as the same becomes better understood by referenceto the following detailed description considered in connection with theaccompanying drawings.

The detailed description provided below in connection with the appendeddrawings is intended as a description of the present disclosure and isnot intended to represent the only forms in which the examples may beconstructed or utilized. The description sets forth the functions of theexamples and the sequence of steps for constructing and operating theexample. However, the same or equivalent functions and sequences may beaccomplished by different examples.

The examples described in the following, may provide a way of changingthe wavelength of light emitted from the active region of asemiconductor laser in a continuous manner. Tuning of the wavelength maybe accomplished within the laser, without need for external cavities andthe like. The controllable output wavelength of the tunable laser asdescribed and the method of tuning are typically not limited tosemiconductor lasers. The concepts presented herein are suitable forapplication in a variety of semiconductors, thin film devices andsystems, transistors, light emitting diodes (semiconductor or polymer ororganic), dielectrics, and the like as a tunable device implementation.

Thus the tunable device concept may not be limited to tuning thewavelength of emitted light. The tunable laser or tunable device can, byintroducing stress and/or strain, be used to tune other parameters suchas the gain of transistors, the phase in integrated waveguides, thedielectric constants and other electronic, magnetic and opticalparameters that are affected by stress-strain in semiconductor or thinfilm materials. Also, tunable lasers would be useful in commercial andmilitary range finding applications such as laser detection and ranging(LADAR). In short the techniques described may be used to producetunable devices that alter outputs in response to a mechanically appliedstress and or strain, and in particular to stresses and/or strainsapplied through an electronically tunable piezoelectric tuning material.In particular it is typically known that piezoelectric materials canallow fine mechanical movement in the angstrom range verses typicallyavailable sensitivities in the micron or millimeter range. As usedherein, the term “stress-strain” includes stress and/or strain.Furthermore, stress includes, but is not limited to, pressure fromhydrostatic pressure, other hydrofluidic effects, and other microfluidiceffects.

FIG. 1 illustrates one example of a block diagram of a tunable deviceassembly 0100, which includes a tunable material or device 0101 that isresponsive to the application of stress-strain, and a tuning material,device or apparatus 0103 which is capable of temporary mechanicaldeformation in response to a particular input control to the tuningmaterial or apparatus 0106. Typically the tunable material or device0101 is controlled by the input control 0105 and in response to theinput control causes the tunable material or device 0101 to produce anoutput of the tunable material or device 0104. Typically if the inputcontrol 0105 to the tunable material or device 0101 is unchanged, theoutput of the tunable material or device 0104 may remain unchanged. Itmay be possible by an adjoining or coupling method 0102 to intimatelycouple the tunable material or device 0101 to the tuning material,device or apparatus 0103. Once the tunable material or device 0101 iscoupled to the tuning material, device, or apparatus 0103, it may bepossible to in a very controllable manner change the output of thetunable device or material 0104 in prescribed manner, with out changingthe input to the tunable material 0105. The tunable material or device0101 may include a semiconductor laser, transistor, or light emittingdiode (“LED”), or any material or device that is capable of being tunedwith application of a mechanical deformation.

To further describe this example, coupled or disposed on to the tuningmaterial, device or apparatus 0103 is the tunable material or device0101. The adjoining or coupling method 0102 may intimately transfer any,all, or only a portion of stress-strains from the tuning material,device, or apparatus 0103 to the tunable material or device 0101. Thusthe tuning material or device or apparatus 0103 produces mechanicaldeformation that may be directly transmitted to the tunable material ordevice 0101. The tuning material, device or apparatus 0103 may be forexample any material, device or assembly capable of producing amechanical deformation, for example a strain actuator such as apiezoelectric material, or its equivalent may be used. The mechanicaldeformation typically provided to the tunable material or device 0101may be stress, strain, or combination of stress and strains. Thussystems, devices and methods have been devised that typically directlyaffect the stress-strain dependent characteristics of the device orlaser of interest which additionally may allow the possible formation ofa monolithic or compact device with the ability to tune the outputparameters of the device in a controllable manner thus forming a newtype of tunable device.

The materials of the tunable material or device 0101 and the tuningmaterial, device or apparatus 0103 which may be substantiallydissimilar, are attached, coupled or bonded by an adjoining method 0102so that the mechanical deformation induced in the tuning material,device or apparatus 0103 may be transmitted to tunable material ordevice 0101. Adjoining dissimilar materials 0102 may be accomplished byan epitaxial lift-off process, wafer bonding, gluing, mechanicalpressure, clamping of the materials, chemical bonding, direct depositionof tunable material 0101 on tuning material 0103, or other equivalentprocesses. These examples are not limited to those in which the tunablematerial is in direct contact with the tuning material or device,because alternative examples that include those having a separatecoupling are encompassed by this description but not explicitly shownhere.

The tunable device assembly 0100 may be activated with an input to thetunable material 0105, such as a bias voltage or current, mechanicalbias or other ways to activate the device. Secondly a way of deformingthe tuning material, device or apparatus 0103 is applied, which mayinclude the application of an input control 0106 to the tuning material.The input control may be a voltage, current, magnetic field, mechanicalpressure, or any input control that allows for the control of the tuningdevice. Because the device and the tuning material may be intrinsicallyattached or coupled, the input control to tuning material 0106 may beintended to transfer the deformation to the tunable material or device0101, such that the characteristic parameters of the device are alteredproducing a tunable output 0104, with out changing the input to thetunable material 0105. The maximum change in the output of tunablematerial or device 0104 may be dependent on the internal material ordevice properties of the tunable material or device 0101 and itssensitivity to the stress and strain applied to it. A more closelycontrolled stress-strain that is applied to the tuning material, deviceor apparatus 0103 may result in more precise control of the output oftunable material or device 0104.

In a first example, the tunable material or device 0101 outputs thetunable output 0104 before the input control 0106 is applied to thetuning material, device, or apparatus 0103, and the tunable material ordevice 0101 generates a tuned or otherwise different tunable output 0104after the input control 0106 is applied to the tuning material, device,or apparatus 0103 and after at least a portion of the stress-strain fromthe tuning material, device, or apparatus 0103 is transferred to thetunable material or device 0101. In a second example, the tunablematerial or device 0101 outputs the tunable output 0104 only after theinput control 0106 is applied to the tuning material, device, orapparatus 0103 and only after at least a portion of the stress-strainfrom the tuning material, device, or apparatus 0103 is transferred tothe tunable material or device 0101. In both examples, the tunableoutput 0104 can be considered to be “varied,” “changed,” and/or“adjusted.”

FIG. 2 shows a block diagram of a tunable laser assembly 0200 which mayinclude a semiconductor laser 0201 capable of being tuned by applicationof a mechanical deformation. In another example, the laser may be asemiconductor quantum well (“QW”) laser.

A tuning material, device, or apparatus 0203 (hereafter referred totuning material 0203) is coupled to the laser 0201 by a coupling, directbonding, transfer/merging, or disposing layer or method 0202, orequivalent. The tuning material may be a strain actuator such as apiezoelectric, a mechanical apparatus for deformation, a magneticdevice, a microelectro-mechanical device, microfluidic device or otherequivalent material. The tuning material 0203 may be used to produce amechanical deformation that may be transferred to the semiconductorlaser 0201. The mechanical deformation may be impressed upon the devicethrough various forces including mechanical, electrical, magnetic, acombination of forces, and the like. The mechanical deformation from thetuning material 0203 is intended to provide stress, strain, orcombination of stress and strain through the coupling method 0202 to thelaser 0201 to change the output wavelength of the laser light 0204, in acontrollable manner without the need to change the input control whichmay be a current bias (I_(bias)), voltage (V_(bias)), or the like 0205to the semiconductor laser 0201. Additionally the laser may also beinput controlled by optical pumping methods. Furthermore both electricalinjection and optical pumping can be operated in continuous wave (“CW”),pulsed, synchronous, or asynchronous modes.

The materials of the laser 0201 and tuning material 0203 may be mergedusing coupling method 0202 in a manner so as to create an intimatecontact or transfer layer, thus enabling the mechanical deformationinduced in the tuning material 0203 to be physically transferred to thelaser 0201. Merging dissimilar materials 0202 may be accomplished by anepitaxial lift-off process, wafer bonding, modified wafer bonding andetching off the substrate, mechanical pressure, gluing, chemicalbonding, direct epitaxial growth of laser or equivalent processes or thelike. Also the merging of dissimilar materials 0202 is not limited tothe process where the laser and tuning material are in intimate contact.A separate coupling layer may be disposed between the tuning material0203 and the semiconductor laser 0201, and falls within this descriptionfor allowing the transfer of the mechanical deformation from the tuningmaterial to the laser. The properties of coupling 0202 can be of verysimilar or dissimilar materials to the tuning material 0203 and thelaser 0201.

The tunable laser assembly 0200 may by applying a bias current(“I_(BIAS)”) or voltage (“V_(BIAS)”) 0205 cause the laser to emit lightat its designed characteristic or fundamental frequency. A control inputlike a tuning voltage (“V_(tuning)”) 0206 may be applied to the tuningmaterial 0203, thus producing stress-strain that may be transmittedthrough the coupling layer or interface 0202 to the tunable laser 0201,and causing the wavelength of the light output 0204 to change in somedefined manner away from the characteristic wavelength. The tuningvoltage (“V_(tuning)”) is but one type of control signal that may beused for controlling the tuning material. For example, electricalcurrents, mechanical controls, magnetic fields and the like may be usedin addition to and/or in place of the tuning voltage as input controlsignals 0206.

Under certain types of stress-strain like compression, the effects ofthe stress-strain on a QW laser for example may shift the output toshorter wavelengths from the unstrained fundamental or characteristicwavelength; and under certain types of stress-strain like tension, mayshift the light emission to longer wavelengths. It may be possible toshift the wavelength under compression to longer wavelengths and a shiftthe wavelength under tension to shorter wavelengths. An unstrained QWlaser can be designed for a given fundamental wavelength such that theintroduction of stress-strain produces shifts around the fundamentalwavelength. The concept however is not limited to a QW laser andincludes other types of semiconductor lasers and devices whosecharacteristics may similarly be tuned.

FIG. 3 illustrates an example of tunable assembly for mechanicallystressing-straining an optoelectronic device, which may include asemiconductor laser. This side view of the figure shows mechanicallyadjoining a laser to a tuning apparatus and stressing-straining thelaser to change output wavelength of laser. Also shown is a depiction ofthe graphical data representing the change in wavelength 0304.Corresponding to the side views are the above respective graphs 0304showing how the stress/strain jig tuning apparatus 0203 may affect thelaser 0201, but this example is not limited to this configuration. Thelaser 0201 may be positioned in a stress or strain jig/clamp 0203 on thebase 0310 in a loosely or more intimately adjoined method such as with agluing or bonding process but the application is not limited to such aprocess. A top plate 0309 is disposed on the top of the laser. The topplate may be loosely coupled or more intimately coupled to the laser0201. Pressure 0306 can be applied to the strain jig/clamp 0203 at thetop plate 0306. The pressure 0306 may include constriction in a vise,application of air pressure, torquing with a screw or micrometerconfiguration, microelectro-mechanical, microfluidic or similar ways.This example shows a way of mechanically stressing-straining the laser,but this does not preclude other ways to achieve the same stress-strainon the laser. Typically the laser 0201 may be input controlled by a biascurrent (I_(bias)) 0305, though other signals such as voltage bias,optical pumping and other variations may be used for input control.These signals may be operated in continuous wave (CW), pulsed,synchronous, or asynchronous modes of operation. The laser 0201 with theapplication of I_(bias) 0305 may output a characteristic wavelength(“λ₀”) 0301, and the light from the laser 0201 may be output from theside of the laser 0201. The dotted box 0304 depicts a possible spectralgraphical output of the laser used to characterize the laser, showing ashift in the wavelength of the laser 0201 due to stress-strain. The box0304 shows the spectral characteristic of the laser 0201, which isusually plotted as light_(out) 0307 (which may be typically power)verses the wavelength 0308. The sharpness of the spectral characteristicis what typically defines a laser 0201. Pressure applied to the laser0201 can change the output wavelength of the laser 0304 from itsfundamental wavelength (“λ₀”) 0301 to a new wavelength (“λ_(new)”) 0302which has been shifted or tuned away from (“λ₀”) with out changing the(I_(bias)) 0305 to the laser 0201 and without substantially changing thesharpness of the spectral characteristic. The manner in which thestress-strain may be applied may determine whether the lasercharacteristic wavelength will shift to shorter or longer wavelengths.Additionally if the top and bottom of the laser are used for inputcontrol of the (I_(bias)) 0305 then the top plate 0309 and the base0310, if they are made of conducting material, may serve as contactpoints for application of the current bias 0305 to the laser, if it isoperated in this manner. Additional monolithic and compact ways ofapplying pressure to tune the wavelength of the laser, may be applied,such as by using a piezoelectric (or equivalent) material.

FIG. 4 shows a side view of an example of a tunable laser assembly 0400with an applied lateral stress-strain 0410 inducing a change in theoutput wavelength of the laser and the depicted laser spectralcharacteristic graphically showing the change in light output of thelaser 0404. The side view drawings of the different laser stress-strainconfigurations correspond to the above graphical depictions of thecorresponding light output graphs 0404.

In this example a semiconductor laser 0201 is coupled, typically bydirect attachment or by equivalent ways, to a tuning material 0203 suchas an exemplary piezoelectric, by wafer bonding, gluing, or by utilizingan intermediary adhesive material such as gold metal in the waferbonding process, but may not be limited by these techniques.

The adjoining method of disposing the laser on to the piezoelectric mayutilize equipment such as a wafer bonder, which may take the laser 0201and the tuning material 0203 and fuse the two materials under heat,pressure, ultrasound to form a monolithic unit. Due to the typicalformation of a strong bond between the laser 0201 and the tuningmaterial 0203, it is possible to directly transfer stress-strain fromthe tuning material 0203 to the laser 0201. Additionally it may bepossible to use an adhesion layer like a glue or a metal which may forman intermediary bond between the laser 0201 and the tuning material 0203thus also forming a monolithic unit where the stress-strain can betransferred directly to the laser 0201.

Typically the laser 0201 may be input controlled by a bias current(I_(bias)) 0405, though other techniques such as voltage bias, opticalpumping and other variations may be used for input control. Thesetechniques may be operated in continuous wave (CW), pulsed, synchronous,or asynchronous modes of operation. The laser 0201 under (I_(bias)) 0405may output a characteristic wavelength (“λ₀”) 0401. In this example thelaser light may occur from the side of the laser or the top of thelaser. The dotted box 0404 depicts a possible spectral graphical outputof the laser by standard measurement techniques used to characterize thelaser, showing a shift in the wavelength of the laser due tostress-strain. The box 0404 shows the spectral characteristic of thelaser, which is usually plotted as light_(out) 0407 (which may typicallybe power) verses the wavelength 0408. The sharpness of the spectralcharacteristic is what typically defines a laser.

The tuning material (or device or apparatus) 0203 produces mechanicaldeformation that may be directly transmitted to the tunable material ordevice 0201. The tuning material 0203 may be for example any material,device or assembly capable of producing a mechanical deformation, forexample a strain actuator such as a piezoelectric material, or itsequivalent may be used. The input control to the tuning material may bea voltage, current, magnetic field, mechanical pressure, or any inputcontrol that allows for the control of the tuning material. The tuningmaterial 0203, is capable of deformation by the application of an inputcontrol which may be a voltage bias at electrodes 0406 which may be onthe sides of the tuning material. The tuning material 0203 may deform inthe lateral direction depending on the application of voltage to theelectrodes 0406, in compression or in tension. The arrows in the figureshow examples of possible directions of deformation for compression andtensile strain. The arrows in the figure for lateral compressively andtensiled stress-strain show one of many possible directions ofdeformation.

The laser 0201 may be biased (I_(bias)) 0405 to produce a characteristicwavelength when the laser 0201 is unstrained, shown graphically in lightoutput 0404 with the emitted output wavelength is typically acharacteristic or fundamental wavelength (“λ₀”) 0401. When a voltage isapplied to the tuning material 0203 through the electrodes 0406, suchthat the tuning material undergoes lateral compressive stress-strain,because the laser 0201 is adjoined to the tuning material, thestress-strain will be transferred from the tuning material 0203 to thelaser 0201. The laser output 0404 may blue shift to shorter wavelengths,such as (λ_(low)) 0402. Conversely, when a suitable voltage is appliedto the tuning material 0203 through the electrodes 0406 such that thetuning material undergoes lateral tensile stress-strain, the laseroutput 0404 may red shift to longer wavelengths, such as (λ_(high))0403. It may be possible that the sequence of the application of lateralstrain to the laser may be different then described. The above exampledescribes a way of tuning by applying forces in a single direction.However tuning may also be accomplished by applying forces in severaldirections at once, such as by bending, twisting or the like.

FIG. 5 shows a side view of an example of a tunable laser assembly 0500with an applied bending, twisting or torquing stress-strain 0510, asinducing a change in the output wavelength of the laser and the depictedlaser spectral characteristic graphically showing the change in lightoutput of the laser 0504. The side view drawing of the different laseroperations correspond to the above graphical depictions of thecorresponding light out put 0504. In this example a semiconductor laser0201 may be coupled, typically by direct attachment, to a tuningmaterial 0203 (such as an exemplary piezoelectric), by wafer bonding,gluing, or by utilizing an intermediary adhesive material such as goldmetal in the wafer bonding process, but may not be limited to thesetechniques.

The adjoining method of disposing the laser on to the piezoelectric mayutilize equipment such as a wafer bonder, which may take the laser 0201and the tuning material 0203 and fuse the two materials under heat andpressure to form a monolithic unit. Due to the formation of a strongbond between the laser 0201 and the tuning material 0203, it may bepossible to directly transfer strain from the tuning material 0203 tothe laser 0201. Additionally it may be possible to use an adhesion layerlike a glue (or a metal) which may form an intermediary bond between thelaser 0201 and the tuning material 0203, thus also tending to form amonolithic unit where the strain can be transferred directly to thelaser 0201.

Typically the laser 0201 may be input controlled by a bias current(I_(bias)) 0505, though other methods such as voltage bias, opticalpumping and other variations may be used for input control. Thesemethods may be operated in continuous wave (CW), pulsed, synchronous, orasynchronous modes of operation. The laser 0201 under (I_(bias)) 0505may output a characteristic wavelength (“λ₀”) 0501. In this example thelaser light may be emitted from the side of the laser or the top of thelaser. The dotted box 0504 depicts a possible spectral graphical outputof the laser (measured by standard measurement techniques) used tocharacterize the laser, showing a shift in the wavelength of the laserdue to stress-strain. The box 0504 shows the spectral characteristic ofthe laser, which is usually plotted as light_(out) 0507 (which maytypically be power) verses the wavelength 0508. The sharpness of thespectral characteristic is what typically defines a laser.

The tuning material (or device or apparatus) 0203 produces mechanicaldeformation that may be directly transmitted to the tunable material ordevice 0201. The tuning material 0203 may be for example any material,device or assembly capable of producing a mechanical deformation. Forexample a strain actuator such as a piezoelectric material, or itsequivalent may be used. The input control to the tuning material may bea voltage, current, magnetic field, mechanical pressure, or any inputcontrol that allows for the control of the tuning material. The tuningmaterial 0203, is capable of deformation by the application of an inputcontrol which may be a voltage bias at electrodes 0406 which may be onthe sides of the tuning material. The tuning material 0203 may deform inthe vertical, bending, twisting or torquing direction depending on theapplication of voltage to the electrodes 0506, in compression or intension. The arrows in the figure for compressively and tensiled bendingstrain show one of many possible directions of deformation.

The laser 0201 may be biased (I_(bias)) 0505 to produce a characteristicwavelength when the laser 0201 is unstrained, shown graphically in lightoutput 0504 with the emitted output wavelength typically at acharacteristic or fundamental wavelength (“λ₀”) 0501. When a voltage isapplied to the tuning material 0203 through the electrodes 0506, suchthat the tuning material undergoes compressively bending stress-strain,because the laser 0201 is adjoined to the tuning material 0203, thestress-strain will be transferred from the tuning material 0203 to thelaser 0201. The laser or light output 0504 may blue shift to shorterwavelengths, such as (λ_(low)) 0502. Conversely, when a suitable voltageis applied to the tuning material 0203 through the electrodes 0406 suchthat the tuning material undergoes tensile bending stress-strain, thelaser or light output 0504 may red shift to longer wavelengths, such as(λ_(high)) 0503. It may be possible that the sequence of the applicationof bending, twisting and torquing stress-strain 0510 to the laser may bedifferent then described. The electronic tuning of a laser describedabove may also be applied in combination with a compact mechanicalfixture to tune the laser.

FIG. 6A shows a side view of an example of a tunable laser assembly0600A with the ability to increase the applied vertical strain 0610A tothe laser 0201, by employing a rigid clamp 0611A and a tuning material0203 such that the laser 0201 can be stressed-strained in the “vertical”direction 0610A inducing a change in the output wavelength of the laserand the depicted laser spectral characteristic graphically showing thechange in light output of the laser 0604A. It should be noted that“vertical” or “lateral” is only used in relationship to the drawing andis not meant as an absolute direction, but more to contrast to the otherexamples described. It should be noted that because one can arbitrarilyorient the tunable laser assembly in any direction, typical directionalsignatures are used only for illustration and not for purposes of anyabsolute direction. The side view drawings of the different laserstress-strain operations correspond to the above graphical depictions ofthe corresponding light out put 0604A. In this example a semiconductorlaser 0201 is coupled, typically by direct attachment, to a tuningmaterial 0203 such as an exemplary piezoelectric, by wafer bonding,gluing, or by utilizing an intermediary adhesive material such as goldmetal in the wafer bonding process, but tunable laser assembly 0600A isnot limited by these techniques. The top of the laser 0201 may also bedirectly adjoined to the rigid clamp 0611A by various describedattachment methods.

Typically the laser 0201 may be input controlled by a bias current,voltage bias, optical pumping and other variations. For simplicity theinput control to the laser 0201 is not shown, but it is typicallyunderstood that the laser normal mode of operation includes inputcontrol methods as described. It should be noted that if one usesoptical pumping as a method of input controlling the laser 0201, thismay eliminate the need for electrical contact pads to laser 0201,because this generally entails using an “additional laser” to opticallypump the laser 0201. The input control techniques may be operated incontinuous wave (CW), pulsed, synchronous, or asynchronous modes ofoperation. The laser 0201 in an unstrained state may output acharacteristic wavelength (“λ₀”) 0601A. In this example the laser lightmay be emitted from the side of the laser. The dotted box 0604A depictsa possible spectral graphical output of the laser by standardmeasurement used to characterize the laser, showing a shift in thewavelength of the laser due to stress-strain. The box 0604A shows thespectral characteristic of the laser, which is usually plotted aslight_(out) 0607A (which may typically be power) verses the wavelength0608A. The sharpness of the spectral characteristic is what typicallydefines a laser.

When a voltage is applied to the tuning material 0203 through theelectrodes 0606A, such that the tuning material undergoes compressivestress-strain, the laser or light output 0604A may blue shift to shorterwavelengths, such as (λ_(low)) 0602A. Conversely, when a suitablevoltage is applied to the tuning material 0203 through the electrodes0606A such that the tuning material undergoes vertical tensilestress-strain, the light output 0604A may red shift to longerwavelengths, such as (λ_(high)) 0603A. The arrows in the figure show thedirection of deformation of the tuning material 0203. It may be possiblethat the sequence of the application of strain to the laser may bedifferent then described. The rigid clamp 0606A allows for furtherincreases in strain to the laser. The “C” rigid clamp 0611A structureallows force to be transmitted from one side of the laser to the other,as the tuning material 0203 which may be a piezoelectric material,operates.

It is typically noted that any variation of stress and/or strain appliedby a tuning material 0203 to tunable material 0201 by the describedstresses or additional variations as torquing stresses-strains orpinpoint stresses-strains may be also possible. Pinpointstresses-strains could be accomplished by having a pointed or roundedend physically in contact with the surface of the laser. Because thestress-strain can be increased dramatically for such small areacontacts, this offers an additional example of a way to form a tunablelaser or device assembly.

FIG. 6B shows side views of additional variations for enhancingstress-strain effects on the laser 0201 to further shift the laserwavelength from its characteristic wavelength in theunstrained-unstressed state. For simplicity the input control to thelaser 0201 is not shown, but it is typically understood that the normalmode of operation of the laser includes input control. Typically inthese geometries the laser light may be emitted from the side of thelaser. The variations shown may incorporate two piezoelectrics 0203 toprovide additional stress-strain and control. Each piezoelectric 0203may be independently controlled for straining the laser 0201, in avariety of manners. This figure shows methods of increasing thestress-strain by utilizing two piezoelectrics for increasing thewavelength tunable range of the laser 0201. Variation (1) utilizes twopiezoelectrics. Variation (2) uses two piezoelectrics and a clamp.Variation (3) is a combination of (1) and (2). All three examples allowfor enhanced wavelength tunability control of the laser. Thesevariations include either intimate bonding and/or mechanical couplingfor the formation of the tunable laser.

Variation (1) shows a tunable laser assembly 0620B for the case thatlaser 0201 may be coupled via a bonding, gluing, or using anintermediary adhesive material like gold to the two piezoelectrics. Thebottom of the laser 0201 is coupled to the top of a first piezoelectric0203, and the top of the laser 0201 is coupled to the bottom of a secondpiezoelectric 0203. Once the laser 0201 is joined to two piezoelectrics0203, independent control of the piezoelectrics 0203 allows foradditional sensitive control for lateral stress-strain induction intothe laser 0201. The arrows show the direction of deformation of thepiezoelectrics. The top piezoelectric 0203 can be controlled first, andthen the bottom piezoelectric 0203 can be turned on. Thus the degree ofstrain can be doubled with twice the control. Also the piezoelectrics0203 can be operated in opposition. Though the example shows apiezoelectric other variations of tuning materials may be used in asimilar fashion.

Variation (2) shows a tunable laser assembly 0630B for the case thatlaser 0201 may be coupled via a bonding, gluing, intermediary adhesivematerial like gold technique to the two piezoelectrics 0203 as invariation (1), but the stress-strain from the piezoelectrics is theapplied to the sample in the vertical direction as shown by the arrows.This type of geometry may utilize a “C” rigid clamp 0611B to maximizethe stress-strain on the laser 0201. Once the laser 0201 is joined totwo piezoelectrics 0203, independent control of the piezoelectricsallows for additional sensitive control for “vertical” or normal to thelaser stress-strain induction into the laser 0201. The top piezoelectric0203 may be controlled by applying the appropriate input control voltageto electrodes 0606B, and similarly the bottom piezoelectric 0203 can beactivated in this fashion, thus the degree of stress-strain can bedoubled with twice the control. The arrows show the deformation of thepiezoelectric 0203. Also the piezoelectrics 0203 can be operated inopposition, yielding very precise control of the stress-strain to thelaser 0201.

Variation (3) shows a tunable laser assembly 0640B for the case thatlaser 0201 may be coupled via a bonding, gluing, intermediary adhesivematerial like gold technique to the two piezoelectrics 0203.Additionally the assembly is placed in a rigid clamp 0611B which allowsfor maximizing lateral and “vertical” strain to the laser as shown bythe arrows showing the possible deformations to the piezoelectrics 0203.

This configuration may be considered a combination of variation (1) and(2), because the top piezoelectric places lateral stress-strain on thelaser 0201 and the bottom piezoelectric 0203 places verticalstress-strain on the laser. Once the laser 0201 is joined to twopiezoelectrics 0203, independent control of the two piezoelectrics 0203allows for additional sensitive control for lateral and vertical straininduction into the laser 0201. The top piezoelectric 0203 may becontrolled first, and then the bottom piezoelectric 0203 can be turnedon by applying an appropriate input control voltage to the electrodes0606B, thus the degree of strain may be doubled with twice the control.The arrows show the direction of deformation of the piezoelectric 0203.Also the piezoelectrics 0203 may be operated in opposition, yieldingvery precise control of the stress-strain to the laser 0201. These aresome variations that can be utilized for making a more versatile tunablelaser system, however other variations may be possible. In addition toapplying mechanical force in a single direction, in several directionsby twisting, by adding a clamp like structure, or by utilizing the clampstructure and one or more piezoelectric materials other devices thatproduce mechanical forces may be included.

FIG. 6C shows additional variations for enhancing stress-strain effectson the laser 0201 to further shift the laser wavelength from theunstrained characteristic wavelength of the laser. For simplicity theinput control to the laser 0201 is not shown, but it is typicallyunderstood that the laser in normal operation typically includes inputcontrol. Typically the laser light may be emitted from the side of thelaser. The variations shown may incorporate a piezoelectric 0203 withanother method of producing stress-strain in the laser, which may resultin additional strain and control. Each piezoelectric 0203 and the secondtechnique of straining can be independently controlled for straining thelaser 0201.

Variation (1) shows a tunable laser assembly 0620C for the case thatlaser 0201 is coupled via a bonding, gluing, intermediary adhesivematerial like gold technique to the piezoelectric 0203 and additionallycoupled to a MEMS device 0615C. The MEMS device 0615C may applystress-strain to laser 0201 via a pointed pressure mechanism which mayutilize an input control 0612C by a voltage. Once the laser 0201 isjoined to two stress-strain devices, independent control of thepiezoelectric 0203 and the MEMS device 0615C allows for additionalsensitive control for lateral stress-strain induction into the laser0201. The piezoelectric 0203 can be controlled independent of the MEMSdevice 0615C thus the degree of stress-strain may be doubled with twicethe input control to produce varying degrees of stress-strain.

Variation (2) shows a tunable laser assembly 0630C for the case thatlaser 0201 is coupled via a bonding, gluing, intermediary adhesivematerial like gold technique to the piezoelectric 0203 and additionallycoupled to a magnetoelastic device 0616C. The magnetoelastic device0616C may apply stress-strain to laser 0201 via a bending, twisting ortorquing mechanism which may utilize an input control 0612C of amagnetic field. Once the laser 0201 is joined to two stress-straindevices, independent control of the piezoelectric 0203 and themagneto-elastic device 0608C allows for additional sensitive control forstress-strain application to the laser 0201.

Variation (3) shows a tunable laser assembly 0640C for the case thatlaser 0201 is coupled via a bonding, gluing, intermediary adhesivematerial like gold technique to the piezoelectric 0203 and additionallycoupled to a microfluidics device 0617C. The microfluidics device 0617Cmay apply stress-strain to laser 0201 via a bending, twisting ortorquing mechanism which may require an input control 0612C of apressure. Once the laser 0201 is joined to two stress-strain devices,independent control of the piezoelectric 0203 and the microfluidicsdevice 0617C allows for additional sensitive control for stress-strainapplication to the laser 0201. The microfluidics device 0617C allows forthe possibility of slowly building up the pressure on the laser 0201 andthus may be minimizing damage to the laser 0201.

Variation (4) shows a tunable laser assembly 0650C the case that laser0201 is coupled via a bonding, gluing, intermediary adhesive materiallike gold technique to the piezoelectric 0203 and additionally coupledto a pressure producing device 0618C. The pressure producing device0618C may apply stress to laser 0201 via a hydrostatic, mechanical, orof like mechanism which utilizes an input control 0612C by a voltage,current, mechanical, or like techniques. Once the laser 0201 is joinedto two stress-strain devices, independent control of the piezoelectric0203 and the pressure producing device 0618C allows for additionalsensitive control for lateral strain induction into the laser 0201.These are some variations that can be utilized for making a moreversatile tunable laser system, but the disclosure is not limited tothese variations.

FIG. 7 is a perspective schematic of a typical edge emitting or in-planesemiconductor laser 0700. The edge emitting laser 0700 may consist of asubstrate 0710 with an active region 0706 disposed between a p-typelayer 0704 and an n-type layer 0705. Cleaved facets on the front 0708and on the back 0709 of the laser typically form a resonant opticalcavity. The order if the layers may not be restricted as describedabove. To activate the laser, a bias current can be applied to top 0702and bottom 0703 metal contacts. Upon application of the bias to thelaser, light of a wavelength A is typically emitted 0707 from the edgeof the laser.

An exemplary edge emitting semiconductor laser may include an indiumgallium arsenic phosphide (InGaAsP) quantum well active region material0706 on an indium phosphide (InP) substrate 0710 for near-infrared (IR)light emission 0707, or their equivalents. The QW active region of thestructure is typically capable of emitting a designed center wavelengthover a wide range of possible wavelengths depending on a number ofdevice design parameters including but not limited to the thickness andcomposition of the layer materials. Being able to tune light over thewide range of wavelengths could be useful for a variety of applications.

The design and fabrication of this type of edge emitting laser structuremay utilize consideration of the material properties of each layerwithin the structure, including energy band structure and bandalignments, electronic transport properties, optical properties, systemsdesign, and the like. An edge emitting laser such as the exemplary onedescribed above may satisfactorily be wavelength tuned in the mannerpreviously described.

It may also be possible to omit the top metal 0702 and the bottom metal0703 and optically pump the edge emitter 0700 from the top, bottom orside with another laser that may have an emission wavelength shorterthan the edge emitter 0700. This may simplify the process sincemetallization of the laser 0700 can be avoided.

FIG. 8 is a schematic of the side view of a vertical cavity surfaceemitting laser (“VCSEL”) 0800. A substrate 0806 may have depositedlayers of p-type distributed Bragg reflectors (“DBR”) material 0803, andn-type distributed Bragg reflector material 0805. An active region 0804is inserted between the DBR structures 0803, 0805. Metal contacts 0802,0807 are provided for applying a bias to the laser. The p-type DBRs 0803and n-type DBRs 0805 form the resonant optical cavity. The order of thelayers is not restricted as described above. Upon application of acurrent bias to the laser, light is typically emitted 0808 from thesurface of the laser. A VCSEL laser 0800 such as the exemplary onedescribed above may satisfactorily be tuned in the manner previouslydescribed, with provision made to allow laser emission from the top ofthe structure rather than from the side, or edge, as in the edgeemitting laser of FIG. 7.

It may also be possible to omit the top metal 0802 and the bottom metal0807 and optically pump the VCSEL 0800 from the top or bottom withanother laser that may have an emission wavelength shorter than theVCSEL 0800. This may simplify the process since metallization of thelaser 0700 can be avoided.

For both the edge emitting laser 0700 and the VCSEL 0800 the inputcontrol to the lasers may be a current bias, voltage bias or opticalpump techniques as described. Furthermore both electrical injection andoptical pumping can be operated in continuous wave (CW), pulsed,synchronous, or asynchronous modes of operation. Next details on tuningapparatuses that may employ a clamping type of device will be shown.

FIG. 9 shows a side view of two variations of a stress-strain jig 0920and 0930 that may act as a tuning apparatus for stressing-straining alaser. Variation (1) acts as a stress-strain jig 0920 with appliedpressure at 0902 to strain the material in the space 0912. The strainjig may employ air, hydraulic, and/or mechanical pressure at point orregion 0902 to physically strain the device by forcing top plate 0903towards strain jig base 0905. The rods 0904 act as sliders so that topplate 0903 can move down in a controllable manner.

Variation (2) of the stress-strain jig 0930 acts as a stress-strain jigwith a tightener 0906 which may be a torquing screw or micrometerassembly or the like, to stress-strain the material in the space 0912.The stress-strain jig may use a tightener 0906 which may or may not bethreaded through top plate holder 0907 to physically stress-strain thedevice by forcing the flat end of tightener 0908 towards base 0909. Theend of the tightener 0908 may be flat, rounded or pointed or any othervariation to produce a stress-strain force to material in the space0912. Two variations among many other possibilities are shown in thisfigure.

It may be possible to employ a MEMS type device like variation 0930 forstressing-straining of the laser. The MEMS device may control a pointedtip that may cause a high level of stress-strain if applied to thelaser. Next further details of the exemplary tuning material that may beused in combination with the above described exemplary lasers andexemplary mechanical fixtures are provided.

FIG. 10A shows tuning material properties 1000A and some of thedeformation characteristics of tuning material 0203 upon application ofa voltage V_(tuning) 0206. An exemplary tuning material may be made fromceramic having piezoelectric properties which would have a built inpolarized field 1001A in the normal state. The tuning material 0203 maybe capable of being deformed by either lengthening 1002A or shortening1003A dependent on the polarity of the voltage applied to the tuningmaterial, and it may be capable of fine deformations usually in theangstrom range. A typical configuration is to build the tuning materialinto a chip-capacitor like structure, having layers of piezoelectricmaterial, interdigitated electrodes, and terminations coupled to theelectrodes. Other tuning material types may be used in differentexamples such, as other types of devices including MEMs,magneto-elastic, microfluidic and the like.

FIG. 10B shows side cut away views of two typical configurations of thetuning material 0203 (of FIG. 10A) made from a piezoelectric material.Example (1) shows a simple piezoelectric 1020B that consists of apiezoelectric material 1003B sandwiched by top contact electrode 1006Band a bottom contact electrode 1007B. The piezoelectric generally has aninternal polarization field direction 1009B denoted by the arrow, andwith the (+) and (−) sign showing the polarity. A voltage is typicallyapplied to the contact electrodes 1006B and 1007B and depending on thepolarity of the voltage will determine the elongation or shrinkage ofthe piezoelectric 1003B. The stress-strain direction 1005B for thesimple piezoelectric 1020B is shown by the double headed arrow. In thesimple piezoelectric 1020B the strain direction 1005B is in line withthe top and bottom contact electrodes 1006B and 1007B.

Example (2) is a sideway cut away view of the interdigitatedpiezoelectric 1030B. This structure consists of a left contact electrode1016B and a right contact electrode 1017B with a piezoelectric material1013B sandwiched between the contacts with interdigitated electrodes1018B. The interdigitated electrodes separate alternating polaritypiezoelectrics dictated by the internal polarization field direction1019B as shown by the arrows. This structure forms a multilayer sandwichof to maximize the strain in the structure. A voltage is typicallyapplied to the electrode contacts 1016B and 1017B which are at the endsof the structure and depending on the polarity of the voltage willdetermine the elongation or shrinkage of the piezoelectric 1006B. Thestrain direction 1015B is shown by the double headed arrow. In theinterdigitated piezoelectric 1030B the strain direction 1015B istypically perpendicular to the line between electrode contacts 1016B and1017B. This allows contact electrodes 1016B and 1017B to be placed outof the way of the direction of elongation or shrinkage of theinterdigitated piezoelectric 1030B, which is in contrast to the simplepiezoelectric 1020B. It should be noted that “top”, “bottom”, “left” or“right” is only used in relationship to the drawing and is not meant asan absolute direction, but more to contrast to the other examplesdescribed.

Piezoelectric materials may be considered unique in that the applicationof a voltage to these structures creates an electric field polarization,thereby distorting the crystal to lengthen or contract depending on thepolarity of the voltage. The piezoelectric elements are versatile inthat they may be capable of attaining large stress-strains, and areoften optimized for large stresses-strains with typical voltages up toaround 100V. Piezoelectric actuators are typically superb for minuteincremental application of stresses-strains to materials because themovement of the actuator can be on the order of 1 angstroms ({acute over(Å)}). A piezoelectric actuator can produce extremely fine positionchanges down to the sub-nanometer range. The smallest changes inoperating voltage can be converted into smooth movements. Motion istypically not influenced by stiction, friction or threshold voltages.Piezoelectrics may be used as tuning material 0203 in the previouslydiscussed examples. Single crystal plates, disks, and rings, areavailable and may equivalently be utilized as tuning materials 0203.Typical finished crystal sizes range 1 to 15 millimeters (mm) laterallyand 0.1 to 2 mm in thickness, but can be designed to almost anydimensions. These are typically adequate geometries to attach to laserchips.

Next the coupling of the exemplary tuning materials to the exemplarylasers will be described.

FIG. 11 is a flow chart of an adjoining or coupling method where thepiezoelectric is placed in a clamping jig 1101 and then the tunablematerial or laser is coupled by direct contact or by an intermediary andthen clamped together in the jig 1102. The intermediary can consist ofan adhesive such as a glue or metal or any variation that allows forattachment of the laser to the tuning material, the piezoelectric inthis case, and it also include processes or methods to make theintermediary coupled tunable material to the tuning materialeffectively. The laser is then intimately coupled to the piezoelectric1103, and the piezoelectric can by the application of an input controlsignal, typically a voltage, directly stress-strain the laser to cause achange in the wavelength of the emitted light from its characteristic orunstrained state. The entire structure forms a tunable laser assembly1104. The tunable laser assembly 0600A of FIG. 6A shows a possiblediagram for final structure 1104.

FIG. 12 illustrates an exemplary epitaxial layer lift-off/bondingtechnique 1200. This technique can be used in the previously describedprocess (1102 of FIG. 11) for attaching an epitaxial layer which may bea semiconductor laser to a tuning material. The epitaxial layer of asemiconductor wafer having a laser disposed in it may be lifted off anddisposed upon a different substrate such as a tuning material. So thatthe laser may be disposed upon the tuning material. The exemplarytechnique is known as epitaxial lift-off/bonding technique 1200. A thinfilm layer like a semiconductor material 1201 consisting of an epitaxiallayer (“epilayer”) 1205 can be grown with a highly selective etchingrelease layer 1207, which may be a thin Indium gallium arsenide layer(InGaAs), which is usually deposited on a substrate 1206, which may be aindium phosphide substrate. Epitaxial lift-off occurs by etching releaselayer 1207 releasing a laser structure from its substrate 1206 by aselective etchant 1209 as shown in diagram 1202. At 1202 the epitaxiallayer is protected by disposed wax 1208 that may add mechanicalstrength.

At 1203 the epi-layer (semiconductor laser) 1205 with the wax 1208acting as mechanical strength together form structure 1210, which thenmay be transferred and bonded to a new substrate, such as the tuningmaterial 0203. The initial bonding typically occurs due to van der Waalsforces between the epilayer 1205 and the tuning material 0203. In step1204 when the clean and flat surfaces of two dissimilar materials arebrought into close proximity there may form an intimate contact betweendifferent materials. When the epilayer 1205 and the tuning material 0203are bonded, the wax 1208 can be removed by a solvent leaving the finalstructure as shown in step 1204. Such a method of attachment may be usedto advantageously couple tunable materials to the tuning material. Thestrength of the adhesion typically depends on the type of materialinteraction. Though van der Waals forces may provide the initialattraction, the bonding strength can be increased in materials withappropriate heat treatment, specialized metals, epoxy or self assembledmonolayers leading to the additional formation of covalent bonds acrossthe bonding interface. These materials may be applied to the exposedepilayer surface 1205 and the exposed tuning material surface 0203 indiagram 1203 before the joining process in diagram 1205. These materialsthat promote adhesion may require additional processes or methods tomake them couple the tunable material and the tuning materialeffectively.

FIG. 13 is a flow chart of the epitaxial lift-off/bonding method wherebya semiconductor laser may be intrinsically coupled to a tuning materialas previously shown in FIG. 12. This process shows further details ofthe process block 1102 of FIG. 11. The epitaxial layer (“epilayer”)lift-off process typically consists of two main components: 1) etchingoff and lift-off of epilayer (laser structure) with an etchant, and 2)van der Waals bonding of the epilayer to the tuning material.

The epilayer (laser structure) may be grown with a highly selectiverelease layer on a substrate 1301. Wax may be placed to cover epilayerfor structural strength, etching and lift-off of the thin epilayer(laser structure) off of the substrate with a highly selective releaselayer on substrate 1302. The thin epilayer with wax may be floated offafter etching with highly selective etchant (acid) and then typicallyplaced in water 1303. The thin epilayer with wax may be placed on thetuning material (piezoelectric) from the water immediately 1304. Beforedirect attachment it may be preferable to apply an adhesion layer to theexposed surfaces to promote bonding. The thin epilayer with wax may bondto the tuning material by van der Waals forces 1305. Just placing thetwo materials together in contact can form a strong bond. Aftersufficient time the epilayer may be bonded to the tuning material, andthe wax may be dissolved in solvent. Heat can be used for additionalbonding 1306. Though van der Waals forces may provide the initialattraction, the bonding strength can be increased in materials withappropriate heat treatment, specialized metals, epoxy or self assembledmonolayers leading to the additional formation of covalent bonds acrossthe bonding interface. These materials may be applied to the exposedepilayer and the exposed tuning material before the direct joining ofthe materials as in step 1304. These materials that promote adhesion mayrequire additional processes or methods to make them couple the tunablematerial and the tuning material effectively. The resulting laser andpiezoelectric assembly acts as a single monolithic device by this methodof formation. Next an alternative method of coupling a tuning materialto a tuned material will be examined.

FIG. 14 shows merging the semiconductor laser and the tuning material(piezoelectric) (1102 of FIG. 11) by an alternative process of waferbonding 1400. Wafer bonding can typically require a very clean oxidefree laser 1404 and tuning material 1405 as in step 1401. In additionthe surfaces are usually very smooth. Wafer bonding generally occurs ina clean environment because dust and particles may disrupt the process.The laser and tuning material may be typically placed in methanol orsome equivalent solvent as in step 1401. The laser 1404 may be disposedonto the tuning material in a solution of methanol to prevent oxidationand then removed and placed in the bonding jig 1408 as in diagram 1402.Here the laser 1404 and tuning material 1405 are bonded using heat 1406and pressure 1407 with what is typically called a “wafer bonder” orbonding jig 1408. Wafer bonding typically occurs with the application ofheat 1406 and pressure 1407 over time as depicted in step 1402. Thetemperatures may vary considerably but may be as high as much as 450degrees Celsius (“C) or higher. The bonding strength may be increased inmaterials with use interfacial materials like glues, adhesives, metals,and self assembled monolayers between the two materials that are to bebonded. Additional use of intermediaries for adhesion may be applied instep 1401 before the laser and tuning material are placed in contact.The use of intermediaries may strengthen the bonding process. The finalstructure is typically strongly covalent bonded between the laser 1404and the tuning material 1405 as shown in step 1403.

FIG. 15 is a flow chart of wafer bonding 1500 which may result in strongbonding of the laser material to the piezoelectric. Laser and tuningmaterial (piezoelectric) to be bonded may be cleaned 1501. This processtypically ensures the strength of the bonding process. It is possible atthis step to add adhesive materials to the exposed bonding surfaces ofthe laser and the tuning material the piezoelectric. Materials such asglues, metals and other intermediary layers may help to promote adhesionof the two materials. For example gold could be evaporated on one orboth surfaces of the materials to be bonded. These materials thatpromote adhesion may require additional processes or methods to makethem couple the tunable material and the tuning material effectively.The assembled materials may be placed together in methanol or someequivalent solvent 1502. The two materials may be placed in contactwhile in the methanol and then placed in the wafer bonding jig 1502. Thebonding jig may be slowly closed to put the laser and tuning materialinto intimate contact. Heat, pressure, ultrasound and time may beapplied by the bonding jig 1504 to the laser and tuning material. Laserand tuning material are strongly bonded together and a tunable laserassembly is formed 1505 Wafer bonding may result in a covalent bondingof the two materials, thus the two materials are typically fullymonolithic and can act as one. After the laser and tuning materials arecoupled together as a monolithic unit, the tuning material can be usedto directly stress-strain the laser to change the output wavelength ofthe laser from its unstrained characteristic wavelength. Another methodof disposing a tuning material on a tuned material may be by directdeposition, which will be described next.

FIG. 16 is a flow chart describing a method of direct deposition 1600 ofsemiconductor or thin film material on the tuning material(piezoelectric), to form a tunable device assembly, without directbonding or transfer. The semiconductor or thin film material, afterdeposition, may be fabricated into a device which is fully adjoined orcoupled to the piezoelectric. The piezoelectric crystal may be verysmooth and cleaned and is typically prepared as substrate 1601. Thepiezoelectric crystal may be placed in a conventionally constructeddeposition system 1602. The deposition system may be metalorganicchemical vapor deposition, molecular beam epitaxy, chemical beamepitaxy, evaporation, sputtering, spin-on or other equivalent types.Deposition parameters of semiconductor or thin film material may bedetermined dependent on the deposition system 1603. More specificallyfor semiconductor lasers, the laser material may be depositedepitaxially onto tuning material (piezoelectric) which may act as a seedcrystal substrate 1604. Typically, the growth sources, temperature,time, and heat can determine how the laser grows epitaxially onto thetuning material (piezoelectric) 1605, but other growth parameters may berelevant. Laser material is typically intimately coupled topiezoelectric 1606. Laser material may be fabricated into laser devicewhile coupled to piezoelectric 1607. Electrodes may be disposed onpiezoelectric for biasing. The laser may be electrically biased, whichwould require electrical contacts, or optically pumped, which would notrequire electrical contacts. As previously mentioned, devices other thanlasers may be tuned in alternative examples. An alternative method tothe above consists of depositing the piezoelectric directly on the lasermaterial. The procedure is similar to the above steps except the lasermay be the seed substrate. Both these methods result in a monolithictunable laser structure.

The adjoining or coupling method 1100 of FIG. 11 may be a method ofmaking a compact tunable laser assembly. The following methods may forma monolithic tunable laser assembly: epitaxial layer lift-off/bondingtechnique 1200 of FIG. 12, wafer bonding 1400 of FIG. 14, and directdeposition of semiconductor or thin film material on the tuning material1600 of FIG. 16. Other types of devices such as transistors may have theoutputs of the device tuned by a similar methodology of disposing tuningmaterial onto the transistor.

FIG. 17 illustrates an example of a tunable device assembly 1700 whereinthe device to be strained and thus tuned is a transistor 1707. Thisfigure illustrates variations of the tunable device assembly methodpreviously described in this disclosure which may be applicable to thistransistor 1707 and other equivalent devices. The transistor 1707 iscoupled to a tuning material 1708 such as an exemplary piezoelectric, bya bonding, adjoining or coupling technique, or equivalent. Thetransistor can be of a semiconductor origin, thin film, or polymer basedor any other exemplary type. This figure shows a side view of an exampleof a tunable device assembly 1700 with an applied lateral strain 1710 asinducing a change in the gain of the transistor and the depictedtransistor gain characteristic graphically showing the change in gain ofthe transistor 1704. The side view drawing of the different transistoroperations correspond to the above graphical depictions of thecorresponding gain out put 1704.

In this example a transistor 1707 which can be coupled, typically bydirect attachment, to a tuning material 1708 such as an exemplarypiezoelectric, by wafer bonding, gluing, or by utilizing an intermediaryadhesive material such as gold metal in the wafer bonding process, butnot limited by these techniques.

Typically the transistor 1707 may be input controlled by a bias voltage(V_(bias)) 1705, though other methods such as current bias and othervariations may be used for input control. These methods may be operatedin DC, pulsed, synchronous, or asynchronous modes of operation. Thetransistor with the application of V_(bias) 1705 may output acharacteristic gain curve (“Gain₀”) 1701. The dotted box 1704 depicts apossible gain output 1711 of the transistor, showing a shift in the gaincurve of the transistor due to stress-strain. The box 1704 shows typicaltransistor characteristics in a graphical plot of gain 1711 verses thebias voltage applied to the transistor 1712. The side view drawings ofthe different transistor stress-strain operations correspond to theabove graphical depictions of the corresponding Gain curves 1704.

When the transistor is unstressed-unstrained such as when no bias isapplied to the tuning material, a characteristic output gain curve(Gain₀) 1701 is generated. As a voltage may be applied to electrodecontacts 1706 to the tuning material 1708, depending on the polarity,the tuning material 1708 may undergo compressive stress-strain, whichmay be transferred to the transistor which may cause the output of gainof the transistor to increase 1702. Similarly, if the applied voltage issuch that the tuning material 1708 experiences tensile stress-strain,which may be transferred to the transistor, the output gain of thetransistor may decrease 1703. It may be possible that the sequence ofthe application of strain to the transistor may be different thendescribed. This method described may be useful for any thin filmmaterial or devices.

Materials that may be applicable for this procedure would include thinfilm transistors, liquid crystal material, organic or polymer componentsthat are used in thin film and light emitting structures, dielectricsand so on. The polymer or organic materials could be directly spun onthe tuning material directly in a further variation of an adjoiningmethod. Since the base is crystalline the transfer of strain directlythrough to the polymer organic may be almost completely transferred. Oneexample could be to use such a device for changing the color of liquidcrystal displays by having the liquid crystal bonded to thepiezoelectric and then deformations in the piezoelectric would changethe apparent color of the crystal. Another variation is to deposit byspinning on or evaporating organic material that makes the components ofan organic LED onto the tuning material. The organic thin films wouldundergo the full strain as the tuning material deformation fromcompression would affect the output light wavelength characteristics.This technique can generally accommodate any thin film material that hasproperties that are strain dependent.

It is typically noted that the laser can be replaced in the examplesdescribed by any device whose device parameters or outputs arestress-strain sensitive, and by replacing the laser in the abovegeometries (as shown in FIG. 17) by that device it is possible to makethat device fully and precisely tunable to control the device parametersor outputs of interest.

The following figures show additional features of the tunable deviceassembly.

FIG. 18 shows a schematic block diagram of a tunable laser assembly plusstrain gage feedback control 1800. For feedback control to ensure theprecise deformation of the piezoelectric 1802, the tunable laser may beintegrated with a conventional calibrated movement sensor (strain gagesensor) 1803 that can be operated in a closed loop feed back circuit fortypically very accurate movement control. The strain gage sensor can becalibrated to accurately measure very precise movements of thepiezoelectric or any material that deforms. The laser 1801 may bedisposed on the piezoelectric 1802. A strain gage 1803 is disposed onthe piezoelectric, typically by a conventional gluing technique. Thestrain gage 1803 sensor can precisely measure the deformation of thepiezoelectric 1802, because as the element is strained, the resistanceof the strain gage material typically behaves in a well controlledmanner. Any deviation or drift from the correct strain of thepiezoelectric 1802 may be detected by the strain gage 1803, and anoutput of the strain gage 1806 which may be a voltage relayed to theinput of strain control 1807. The conventional strain control feedbackelectronics 1804 may utilize a conventional phase lock loop to deliver acorrection signal, output of the strain control 1808, which may be avoltage. The output of the strain control 1808 is then relayed to theinput control of the piezoelectric 1809, which will then be adjusted tostabilize the position or deformation of the piezoelectric. Because thelaser 1801 may be very sensitive to stress-strain, any erroneousdisplacement of the piezoelectric 1802 may cause an incorrect shift inthe light out 1810. Such a circuit integrated to the tunable laser wouldassist in wavelength stability of the laser. A wavelength meter (notshown) to measure the light out 1810 of the laser 1801 could be usedindependently or for additional input to the strain control 1807. If awavelength meter is used to measure the wavelength of the light out1810, then it may be possible to use the output from the wavelengthmeter to control the output of the strain control 1808 to deliver theprecise input control of the piezoelectric 1809 to deform thepiezoelectric 1802 to deliver the correct strain to the laser 1801 todeliver the correct light out 1810 wavelength.

FIG. 19 shows a block diagram of a tunable laser plus thermoelectrictemperature control 1900. The laser 1901 may have some temperaturedependent properties, thus to eliminate potential problems a feedbacktemperature control circuit may be useful to stabilize the temperatureof for the tunable laser. The conventionally constructed thermometer1915 may be a calibrated resistor with a known temperature dependence.As the temperature changes the output of the thermometer 1906, which maybe a resistance, will shift and be relayed to the input of theconventionally or custom constructed temperature control 1907. Thetemperature control feedback electronics 1916 may utilize aconventionally constructed phase lock loop to deliver a correctionsignal at the output of the temperature control 1908, which may be avoltage, which is then relayed to the input control 1909 of thethermoelectric 1917, which then adjusts the heating or cooling power.The thermoelectric 1917, thermometer 1915 and the laser 1901 may bedirectly thermally linked together by a conventional thermal conductor1905. Such a circuit integrated to the tunable laser would typicallyassist in wavelength stability of the laser, ensuring the light out 1910may be stable. A wavelength meter (not shown) to measure the light out1910 of the laser 1901 may be used independently or for additional inputof the temperature control 1907. If a wavelength meter is used tomeasure the wavelength of the light out 1910, then it may be possible touse this output signal from the wavelength meter to control the outputof the temperature control 1908, to deliver the precise input control ofthe thermoelectric 1909, to increase or decrease the heating power tothe thermal conductor 1905, to correct for stress-strain wavelengthshifts of the light out 1910 of the laser 1901.

Various methods of feedback control have been described in FIG. 18 andFIG. 19. These methods have been utilizing a piezoelectric for straincontrol of the laser and a thermoelectric for temperature control of thelaser. The input control parameters for the strain control electronics1804 for the case where a piezoelectric 1802 is used have been straingage 1803 or output wavelength of the laser. The input controlparameters for the temperature control electronics 1916, for the casewhere a thermoelectric 1917 is used, have been output of the thermometer1906 or output wavelength of the laser. It is typically noted that theseare not the only methods of feedback control and one method does notpreclude the other. The strain control feedback electronics and thetemperature control electronics could also be employed together to getboth control of strain (and/or stress) and temperature of the laser.Also the inputs used for feedback can utilize other elements and are notlimited to the methods or devices described.

A further adaptation of the methods of feedback control involve usingthe strain control as a method of crude wavelength and using thetemperature control as a method of fine tuning the wavelength of lightemitted from the laser. This method can be a variation of combining bothFIG. 18 and FIG. 19 for wavelength control of the laser. Generallybecause stress-strain can dramatically affect the output of the laser,strain control could be used as a rapid method of achieving the desiredwavelength of the laser. The input control for the strain controlfeedback electronics could be either the output of the strain gageand/or the wavelength light output from the laser, but coarse inputcontrol is not limited to these techniques. Generally becausetemperature shifts in the laser allow for small shifts in outputwavelength, it may be possible to utilize temperature control of thelaser to produce fine control of the output wavelength. The inputcontrol for the temperature control feedback electronics could be eitherthe output of the thermometer and/or the wavelength light output fromthe laser, but the fine input control is not limited to thesetechniques. This method can be an additional variation to control theoutput wavelength of the laser. It is typically noted that theseexamples in no way limit the scope and coverage of this patent.

One of many possible applications of employing the tunable laserdescribed may be in the area of telecommunications. One area that thistunable laser may offer considerable advantages are in wavelengthdivision multiplexing (WDM) for telecommunication applications. WDM is apossible method to increase the bandwidth of a given fiber-optic cable.This technique may require the transmission of signals at differentwavelengths, which may require a fixed wavelength laser at eachwavelength. If single wavelength lasers are used, this scheme adds costand complexity because many additional lasers need to be manufacturedand monitored. The tunable laser described above could possiblyalleviate this problem, because this single tunable laser could possiblyreplace any number of fixed wavelength lasers, offering a significantreduction in cost and complication. Typically a method like this couldbe called one-time provisioning.

Additional applications in telecommunications for the tunable laserdescribed may be for dynamic reconfiguration. High-speed communicationscan be interrupted by a failure of an optical link. In WDM systems thismay require back-up lasers at each wavelength to prevent significantdown time. A tunable laser as described above may be a cost effectivesolution as the back-up allowing for remote reconfiguration and allowfor immediate fixes. In one example the back-up laser can be a compactor monolithic tunable laser, as described above.

The compact or monolithic tunable laser as described could be possiblyused for adding optical networking functionality. Here for add dropnodes a this compact or monolithic tunable laser with a tunable filterallows for selective choice of signals to be added or dropped, there bylowering cost and making better use of bandwidth. Secondly it may bepossible to provide for the dynamic allocation between the transmittingnode and the receiving node to be streamlined with the use of a compactor monolithic tunable laser and filter because all the signals aretransparent except for the signal of interest.

For highly secured fiber optic applications the compact or monolithictunable laser described, which could be employed in a frequency hoppingor wavelength hopping mode method, similar to spread spectrumcommunications. In this example, the compact or monolithic tunable laserwould send signals at a prescribed sequence of specific wavelengths thatmay be based on a key, thus encryption of the signal at differentwavelengths. Also a time key may be employed, which would designate at agiven time which wavelength the signal may be sent, then a very securecommunication method may be developed that would further increase thesecurity of fiber optic systems. In this example even if the opticalfiber carrying the wavelength of light is cut and spliced with a spyingdevice, the intruder would need to know the encryption key to interpretthe signal being transmitted through the optical fiber. Also the use ofthe compact or monolithic tunable laser would allow for sending of falsesignals at a variety of wavelengths to further encrypt the data.

These applications of the compact or monolithic tunable laser are justpossible applications and do not limit this patent in any way.

The following figures show possible implementation of the compact ormonolithic tunable laser assembly for telecommunications.

FIG. 20 shows a block diagram of the possible use of the tunable laserassembly for applications in telecommunications, such as wavelengthdivision multiplexing (WDM), but not limited to these applications.Example (1) shows an electrical modulator with tunable laser assembly2020. The conventional electrical modulator 2009 provides the signalwaveform 2015, which may consist of on-off current pulses, which can besent to the laser input 2005. The laser's light out may then consist ofdigital signals 2010. The wavelength of the laser 2001 may be changed bythe application of a voltage V_(tuning) 2006 to the piezoelectric 2003,which will cause a strain from the piezoelectric to the laser. By beingable to send digital light pulses and also the capability of changingthe wavelength allows the possibility of this laser system 2020 to beused in telecommunication WDM or dense wavelength division multiplexing(DWDM).

Example (2) shows a conventional optical modulator with tunable laserassembly 2030. One possible method of sending digital photonic data withthis laser system is to apply an I_(bias) to the laser, in CW operation.Thus the light intensity is typically relatively constant with theapplication of voltage V_(tuning) 2006 to the piezoelectric 2003 resultsin a deformation of the piezoelectric which due the coupling of thelaser may be directly applied to the laser, thus possibility causing awavelength shift. The light output from the laser 2001 is light out CW2012. This light is then sent to the optical modulator which has thesignal waveform 2015 applied to its input. This may result in the directmodulation of the CW light out 2012 from the laser 2001. Thus it ispossible to produce a digitized light signal 2010 with the addedadvantage that the wavelength of light may be changed thus offering thepossibility of use in DWDM telecommunications systems. By no means arethese two examples encompassing and many other variations are possible.

The tunable devices and their methods of manufacture and use disclosedherein may be implemented in a variety of examples. Therefore, theforegoing discussion of these examples does not represent a completedescription of all possible examples. As an example of an additionalexample, the tunable lasers disclosed herein can be capable ofoutputting any wavelength of light and are not limited to outputtinglight in the visible spectrum. Accordingly, the disclosure of examplesherein is intended to be illustrative of the scope of the disclosure andis not intended to limit the appended claims. Instead, the scope of theinvention shall be limited only to the extent that may be required bythe appended claims.

All elements claimed in any particular claim are essential to theinvention claimed in that particular claim. Consequently, replacement ofone or more claimed elements constitutes reconstruction and not repair.Additionally, benefits, other advantages, and solutions to problems havebeen described with regard to specific examples. The benefits,advantages, solutions to problems, and any element or elements that maycause any benefit, advantage, or solution to occur or become morepronounced, however, are not to be construed as critical, required, oressential features or elements of any or all of the claims.

What is claimed is:
 1. A tunable laser comprising: a first tuningmaterial with stress-strain dependent properties; a tunable materialconfigured to output a light and located adjacent to the first tuningmaterial, the tunable material further configured to bestressed-strained by the first tuning material to adjust the output ofthe light from the tunable material; and a clamping structurecomprising: a first plate adjacent to a side of the first tuningmaterial that is opposite the tunable material; and a base adjacent to aside of the tunable material that is opposite the first tuning material.2. The tunable laser of claim 1, wherein: the first tuning material isin direct contact with the tunable material.
 3. The tunable laser ofclaim 2, wherein: the first tuning material is coupled to the tunablematerial independent of the clamping structure.
 4. The tunable laser ofclaim 1, wherein: the clamping structure is configured to stress-strainthe tunable material to adjust the output of the light from the tunablematerial.
 5. The tunable laser of claim 4, wherein: the first plate ofthe clamping structure is configured to be movable relative to the baseof the clamping structure to stress-strain the tunable material.
 6. Thetunable laser of claim 1, wherein: the first plate is coupled to thebase.
 7. The tunable laser of claim 1, wherein: the first tuningmaterial stress-strain the tunable material based on a voltage or acurrent passed through the first tuning material.
 8. The tunable laserof claim 1, wherein: the first tuning material is piezoelectric.